Motors may be classified into a direct current (DC) motor and an alternating current (AC) motor depending on power used. The DC motor has a commutator and a brush. Due to a mechanical contact between the commutator and the brush, reliability of the DC motor is lowered and a lifespan thereof may be shortened.
An electronic switching type brushless DC (BLDC) motor using a semiconductor device also has been used. The BLDC motors may be classified into an interior rotor type and an exterior rotor type according to an arrangement of stator and rotor.
The interior rotor type motor either uses a rotor that a rotation shaft is inserted into a center of a cylindrical permanent magnet, or uses a so-called interior permanent magnet type rotor that a rotation shaft is inserted into a center of a rotor core having electrical steel sheets stacked thereon and then a plurality of permanent magnets are inserted in the rotor core.
The interior permanent magnet type rotor has a core which a plurality of circular electrical steel sheets are stacked for insulation. The core includes a shaft hole formed through a center thereof such that a rotation shaft can be inserted therein, and permanent magnet insertion portions passed through a periphery of the shaft hole such that a plurality of permanent magnets can be axially positioned therein. The stacked core may be welded to maintain its stacked state or be fixed by using coupling members coupled through each electric sheet plates in an axial direction.
The interior permanent magnet type rotor has flux barriers defined at both end regions of each permanent magnet for reducing a leakage of flux of each permanent magnet.
However, in the related art interior permanent magnet type BLDC motor, the flux barriers are positioned at end portions of each permanent magnet for reducing the flux leakage out of the permanent magnets. When a rotor rotates fast, stress is concentrated on regions of the flux barriers that is configured to have relatively thin ribs due to a centrifugal force, thereby causing deformation and damage of the rotor.
If the thickness of ribs of each flux barrier region is increased to overcome the above problem, the flux leakage of the rotor is also increased, resulting in the lowering of motor performance.